Preeclampsia (PE) is a disease, which affects 5-7% of all pregnancies and is characterized by severe hypertension, proteinuria and edema. Endothelial dysfunction plays an important role in the pathogenesis of this disorder; however, the etiology and mechanisms are still unknown. We recently found that placentas from preeclamptic patients produce an excess of a naturally occurring anti-angiogenic protein, sFIt-1 (soluble fms-like tyrosine kinase-1), resulting in increased serum levels in patients with PE as compared to normotensive pregnant women. Fit-1 is one of the tyrosine kinase receptors for vascular endothelial growth factor (VEGF) and placental growth factor (PIGF). sFIt-1, a secreted splice variant of Fit-1 (lacking the transmembrane and cytoplasmic domains) potently antagonizes VEGF and PIGF, by preventing their binding to the cell-surface receptor. Moreover, we have found that the ratio of anti-angiogenic (sFIt-1) to pro-angiogenic (VEGF + PIGF) proteins in the maternal bloodstream at the time of delivery is substantially elevated in preeclamptic women as compared with control pregnant women. In vitro, preeclamptic serum but not normal pregnant serum induces endothelial dysfunction due to excess sFIt-1, which can be rescued by exogenous VEGF and PIGF. Finally, we have preliminary data that administration of exogenous sFIt-1 to pregnant rats induces hypertension, heavy proteinuria and glomerular endotheliosis, the classic lesion of PE. We therefore hypothesize that alteration in the angiogenic balance due to excess sFLt-1 results in the development of PE. This proposal aims to clarify the role of sFIt-1 and altered angiogenic balance in the pathogenesis of PE. We will first characterize our sFIt-1 induced animal model for PE and will test several therapeutic compounds in an attempt to find new treatment options for patients with PE. We will then elucidate the mechanisms of systemic vascular dysfunction and placental cytotrophoblast dysfunction induced by excess sFIt-1 and altered angiogenic balance using both in vitro and in vivo experiments. Finally, we will focus on studying the transcriptional and post-transcriptional regulatory mechanisms of sFIt-1 production by placental cytotrophoblasts. These focused studies will form the beginnings of a framework for understanding the role of angiogenesis-related gene products in pathogenesis of PE and for exploring novel avenues for the treatment of PE.